This invention relates to a process for producing stainless steel having a bright surface. More particularly, it relates to producing stainless steel having a bright annealed-like surface without the need for annealing in a controlled atmosphere.
Austenitic and ferritic stainless steel strip is conventionally produced by converting an ingot of the steel to a slab which, after conditioning, is rolled on a continuous hot-strip mill to produce a hot-rolled band of intermediate gauge. The hot-rolled band is then cold rolled to final gauge. After cold rolling to final gauge, the surface of the stainless steel strip is bright and glossy. For various final product applications, it is necessary to preserve this surface finish. After cold rolling, however, it is also necessary to anneal the cold-rolled strip to recrystallize the cold-rolled structure and obtain a stress-free product. For austenitic stainless steel, this generally requires annealing temperatures on the order of 1900.degree. to 2000.degree. F. and for ferritic stainless steel temperatures on the order of 1500.degree. to 1600.degree. F. To preserve the cold-rolled surface finish during such annealing, it is performed in a controlled atmosphere furnace wherein both the atmosphere and dew point are regulated. Specifically, the furnace atmosphere may be hydrogen, hydrogen and nitrogen or cracked ammonium (75% hydrogen+25% nitrogen). Controlled atmosphere furnaces of this type are termed " bright annealing furnaces". The strip is passed continuously through the furnace during the annealing operation. Bright annealing cannot be performed in a batch-type furnace wherein the strip is in coil form because the convolutions of the coil will weld together during annealing to impair the surface finish of the strip.
What is needed is a method to produce bright surface stainless steel of comparable surface quality to bright annealed stainless steel which is produced by conventional practices using a controlled atmosphere furnace. It is desirable to do so without capital cost of extensive new equipment, but through modification of existing facilities and processes.